Focus Shift

Nowhere in the world of sending a fly out there with a line you can find rod load being more glorified than in the spey casting scene. Everything seems to gravitate around that. If the cast is good it is because the rod was properly loaded. If it went wrong… well, sure it is due to the rod not having enough load or unloading prematurely.

Sometimes it is possible to get more clues from the analysis of a bad cast than from a perfect one. That is the case with the casts depicted here. The video and pics show a pretty common occurrence that will be used to point out some keys of spey casting mechanics. Take them just as a brief introduction to following articles which will get deeper into that subject (slow motion clips and some not-that-heavy-physics included).

The scenario is the forward cast of a spey characterized by some kind of V-Loop that we will call 7-Loop (thanks to Simon Gawesworth). An extreme 7 for that matter.

Let’s say that you set a nice V-Loop, make the cast and present the fly on target.
On the next cast you manage to get a 7-Loop and the fly falls short of the target on top of a heap of line and leader. That is just one of the possible outcomes of that loop configuration -as it is a fat loop, a tailing loop or even the three of them combined- if the caster doesn’t compensate his stroke to adapt. Even if he modifies his stroke successfully the 7-Loop is still inefficient due to the amount of wasted energy.

The following gif made from a couple of pics from a still camera will shed some additional light.

We could look for an explanation to the inefficiency of that 7-Loop in the gif above in the usual way, basing our analysis in the behaviour showed by the rod. It would go along the following lines.

What happened to this cast?

Hmm, probably the rod didn’t get loaded… but I see a pretty good bend, though!

However, is that a properly loaded rod? Who knows? I, for one, don’t have a clue nor have met anybody capable of quantifying whether a given load is enough for a given cast or not. If only because you can make a cast to the same distance with the same rod and line with rather different loads.

Well -you say to yourself- it could be that the rod got unloaded prematurely due to the anchor slipping… but the loop’s rod leg looks pretty straight, whereas the rising tip of an early unloading would have set a wave in it!
As shown here:

Hmm, we are not getting very far with that approach.

So let’s address the issue from a different standpoint, forgetting the rod and putting the accent in the line.

From the gif above we can quickly draw some visual clues:

A totally ineffective anchor due to the angle of attack.
Only part of the leader is in contact with the water, moreover the angle at which the loop pulls on the anchor makes the latter specially prone to slipping. See how at the end of the stroke the apex of the loop still hasn’t moved forward due to the slipping anchor! In fact it moves a little bit backward! It is a perfect case of a loop propagating but not traveling (but that will be the subject of another article).

The amount of line in the rod leg of the 7-Loop.
The length of line in the rod leg at the start of the stroke is very very short. The longer the piece of line we propel during the casting stroke (the “live line” so to speak) the more efficient the cast:

The reason for that inefficiency has already been covered in this previous article. You can also relate it to the case when we rush the forward stroke of an overhead cast and start it with the line still half its way backwards.

So, compared to a proper V-Loop configuration, for presenting the fly at the same distance a 7-Loop:

Will ask for a higher rod butt acceleration, as a way to give enough momentum to the comparatively shorter length of “live line” we propel during the stroke, to carry a comparatively longer length of “dead line”. That is the reason why the “dead line” to “live line” ratio is key regarding efficiency: the longer the live line the better.

Anchor slipping wastes energy: the line moving backwards goes in the opposite direction of the target, and it doesn’t move by itself so it detracts from the energy needed to move the line forward.

Obviously the longer the cast the higher the impulse you need, which may result in a bigger load, but load is a byproduct of our force application to give the line enough momentum. It really isn’t our goal.

Given that the function of the casting stroke is to give enough velocity to the line in the right direction, it is better then to shift our focus from the rod -which says very little- to the line -which speaks volumes.

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12 comments on “Focus Shift”

In another part of the space time continuum someone asked why the uneven distribution of tension in a D Loop mattered suggesting, of course, that it did not matter. I have been trying to work out why it does because intuitively it seems like it should matter. This article got me a step closer. Hopefully!

(Checked the rule book for this blog and it didn’t say anything bad about thinking without knowing, though it’s fair to assume that knowing without thinking is frowned upon.) :^)

I can readily see and agree with the distinction of live line from dead line and more force/work required to make a fundamentally less efficient cast than an overhead cast. What I struggle with a bit is the idea (which showed up in comments on Roll Cast v Overhead Cast) that it’s the mass in the live line v. the mass in the dead line that makes all the difference. Why? Two reasons.

1) Ignoring the tapered bits for a moment the mass distribution of the line is the same whether it is in a D Loop or stretched out behind us in a completed backcast. If it’s about the relative mass of the live line (under some tension) having to move the mass of the dead line (under SFA tension) then that’s a different thing though still I’m not convinced the inefficiency is just about mass. (Fair enough if have misunderstood the point but if I haven’t it could be another example of how invasive and persistent the idea of rod as spring thing is.)

2) I am wondering if the crucial difference is in the tension of the different parts of the line and it is the relative distribution of tension rather than mass (from rod tip to fluff or fly) that makes the line dead or alive. In a sense then, the slipping anchor and line moving backwards is not just an energy thief, it is “negative” tension. I cringe saying that because I cringe at “negative growth” but hopefully my crime will be forgiven.

I am as guilty as anyone of thinking without knowing, so feel free of sharing your thoughts here.

I don’t base my analysis in line tension because I am lost in that regard; even mor lost than with any other of my musings on physics. So I don’t have an answer for you just a couple of points to add to the brainstorm.

“In a sense then, the slipping anchor and line moving backwards is not just an energy thief, it is “negative” tension.”

Well, as Grunde pointed out in his recent and very interesting contribution to the subject of anchor, tension and load, the slipping anchor putting the fly leg in motion in fact increases tension in the loop, since that tension is proportional to the difference in speeds between both legs.

Back to my point I think that a simile will illustrate it much better than any other attempt in physics. I devised this example to use in my spey classes and have the intention of shooting some slo-mo with it.
You have two balls: tennis and ping-pong. You glue them together with a drop of Loctite. Taking that combo in your hand you throw it forward for maximum distance. You reach 20 m.
After that successful try you separate the balls from each other.
Take the tennis ball and throw it again. You reach 20 m again.
Now you take the ping-pong ball. I encourage you to use as much force as humanly possible and then even more. Accelerate like crazy. Whatever your effort the ball falls 8 m away.
Think of the ping-pong ball as a comparatively short live line, and the tennis ball as a comparatively long live line.
Our limit is power, we can’t accelerate as much as we want. So, in this world of spey casting, increasing the applied force by means of increasing the acceleration of a small mass has more limitations than increasing the applied force by means of accelerating a bigger mass at a lower rate.

No tension in my explanation. However I am also always trying to learn so am open to any further contribution along that line. Even glad of being proved wrong: that would mean that I have learnt something new.

Thanks.

Forgot something interesting about mass distribution that nobody mentions. There is a big difference in the position of the center of mass of the line in a roll compared to a jump roll.

Agree with most, but the wave from a tip rising, won’t happen without the dip beforehand. There’s a reason it’s almost impossible to make a tail with a broomstick or handcasting…. Think I’ve said that before 😉
Otherwise great post B-)
And a pleasure to read

Lasse,
I knew when I wrote about the rising tip that you’d be lurking. 😈
We must discuss that in the future. At the moment I have my head in some other place full of anchors, and it isn’t a port (though I work in one). 😜

On the other hand very glad that you agree with the rest. I am not off track then.

A 7 loop in spey casting is what a tailing loop is in overhead casting: A mistake. So IMO a 7 loop is the consecuence of a bad casting. In the gif and video above both casts has an anchor ahead of the caster…to much in my opinion, so you make a 7 loop becuase you don’t have room enoguht to move the line, and the consecuence is an inefficient cast. I agree with almost all that Aitor explain here but for me it’s important to say that the 7 loop is a consecuence of bad casting. For example: In the gif, this same V loop with a proper anchoring will ends into a perfect cast.:-)

I would like to take one exception to what you said in your September 11, 2015 at 2:15 response to Mark. It may sound picky but I believe it is very important particularly when thinking about all but overhead casts. When talking about throwing the ping-pong ball you said “I encourage you to use as much force as humanly possible and then even more.” The problem is you can’t use force you can only generated it. Your next sentence, “Accelerate like crazy,” is what is really needed.

The point here is that the force generated is a function of accelerating the mass. The mass of the ping-pong ball is fixed so acceleration is the key generating force. Generally overhead cast are dealing with a fixed mass so acceleration is the key. But even overhead cast don’t incorporated all the mass until all of the slack is out, which is source of may overhead casting problems. The physics of Spey casts (roll and switch cast why aren’t they spey cast too?) is fundamentally different. Not only does the caster control the acceleration but they also control the amount of mass being accelerated. So the caster has to maximize the recruitment of mass into the cast through the geometry of the line at the point at which the cast begins. The 7-loop puts too little mass in the cast leaving too much mass to be accelerated by the live line. It’s a geometry issue.

Yep. We are on the same page.
In my turn of being picky I’d say that in a spey cast we can control the amount of line mass being accelerated… up to some extent. Increasing the length of live line is has a practical limit efficiency wise: lenghthen it… while the anchor holds!

I totally agree that there are practical limits in the percentage of line mass you can get into the D-Loop. But I am reminded of a video I saw on YouTube when I was just starting to teach myself spey casting. The caster was switch casting and placing his anchor way behind him to the point that a little further and the cast would have become a sloppy overhead cast. The real limitation arises when a change of direction is to be made. This requires that the anchor point, the D-Loop and the final line delivery stroke direction be in more or less in the same plane. To maximize the live mass in the D-Loop the anchor should be as far away from the target as possible. Here in lies the rub. Because there is a change of direction there is a practical limit as to how far from the target the anchor can be. As the anchor moves away from the target it means that the caster must place the line setup stroke closer and closer to themselves. The limit of anchor placement is reached when they hit themselves with their own back cast. So this limits the live line mass of the delivery stroke. With a 7-loop we are just too far away from this limit than we need to be.

So making the live part of the D loop as long as possible increases efficiency. Obviously the way of achieving the longest live part of a D loop is… to get rid of the D loop, i.e. making an oval cast instead of a spey. But if we are using spey it is for a reason; the most usually stated is lack of space for a conventional backcast, but there could be other reasons for using that technique even when we have enough room behind us: maximizing the time the fly is in the water, avoiding the hassle of having a heavy fly around our head, etc. So we have a D loop which has to be anchored.
Where should we position the anchor for the highest efficiency? We know that the longer the live line the better. Is there a limit, even in a jump roll, in which we don’t change direction? Yes, there is.
When we position the anchor too far backwards it will slip. That slipping wastes energy, and that waste counteracts the advantages of the longer live line we got in the first place.
How is energy wasted by anchor slipping?
– Part of the dead line that should move forward moves backward. It doesn’t move by itself, it does move using the energy intended to displace it in the opposite direction.
– Eventually that dead line moving away from the target must reverse direction, and for that some portion of our energy is used in fighting a backward momentum that doesn’t exist in a holding anchor scenario.
– When finally the end of the line is being pulled in the direction of the target it is farther away from it than in a holding anchor scenario, wasting some more energy in the process.

This phenomenon has been shown here:

At the moment I am working in some new footage and articles to get deeper into this.